Radio frequency identification (RFID) is used in a wide variety of logistics, supply chain, manufacturing, and other applications. For some RFID protocols the reader may modulate commands onto a radio frequency (RF) carrier signal and the RFID tags respond to the modulated commands. Often the tags use simple backscatter modulation, which requires the RFID reader to provide a carrier signal for the tags to reflect their data back to the reader.
Passive backscatter radio frequency identification (RFID) systems use the reader's transmit signal to power the tags. In most countries there are regulatory limits on how much RF power the reader can radiate. The maximum RF output power, together with the minimum activation power of the tag, determine the maximum path loss between the reader and tag. Beyond that maximum path loss the tag does not get enough RF power from the reader to operate. Given the regulatory limits on radiated transmit power and sensitivity limits of tags, the maximum read range of passive backscatter RFID tags in the ultra-high frequency (UHF) range is about 10 to 15 meters. Because of this limited read range, there are often many readers and antennas installed to provide the desired coverage. This can create a serious interference problem for readers, since the reader's receiver must simultaneously decode the very low power backscatter responses from the tags while also receiving the very high power interference from nearby readers. Because of this, linearity is important in RFID receiver design.
In addition to the reader's maximum radiated power and the tag's minimum activation power, the tag's radar cross section modulation depth determines how much modulated backscatter signal power is returned to the reader. These three parameters: transmitter power, tag sensitivity, and tag radar cross section modulation depth, determine the required sensitivity of the RFID reader's receiver.